With a disk array apparatus for controlling, for example, writing of data to a plurality of hard disk drives (hereinafter sometimes referred to as HDDs [Hard Disk Drives])), a support capacity of the disk array apparatus itself increases significantly along with an increase of the capacity of the HDDs and the number of the mounted HDDs. However, performance of a controller for controlling the HDDs cannot sometimes respond to the increase of the capacity of the HDDs.
So, Patent Literature 1 provides a high-performance disk array apparatus by virtualizing a plurality of disk array apparatuses across physical boundaries as one storage system.
Furthermore, Patent Literature 2 discloses a technique that provides a virtual volume (VVOL: Virtual Volume) corresponding to a virtual machine (VM: Virtual Machine).